The first step is to log in to your Gmail
account and notice that down the left side
of the screen is a list of your folders
(Inbox, Starred, Sent Mail, etc) and,
just below it, Contacts. Click on that

Now you're looking at a page that shows you a list of frequently mailed contacts and has a second tab for All Contacts. On the top of that page, you'll see this:

Now Notice the rightmost option Export.
Click on that and you'll see a
helpful pop-up window: